Tuesday, June 27, 2006

Something I saw in Tioman in October 2003. Was on a speedboat enroute from Tekek to Salang when we spotted this in the far horizon. Picture below has been cropped and slightly enhanced to show the funnel more clearly. I believe it is not classified as a waterspout yet as explained in the following section below:

Cobbled from the internetA waterspout is an intense columnar vortex (usually appearing as a funnel-shaped cloud) that occurs over a body of water and is connected to a cumuliform cloud. In the common form, it is a nonsupercell tornado over water.

Scientific work over the last 30 or so years has led to a more complicated picture with waterspouts differing in some ways from tornadoes over land, especially large ones.

Waterspouts and all the different kinds of tornadoes have a similar basic structure with air moving upward. At the ground or ocean surface, winds are rushing faster and faster as they swirl into the vortex and then upward. Often with both tornadoes and waterspouts, the vortex is seen coming down from the cloud, but not obviously touching the ground or ocean. Such vortices that don't seem to touch the ground are called "funnels" or "funnel clouds."

It's important to say "seems" not to touch because often, especially in the beginning, the vortex is invisible along part of its path. We begin to see the vortex when its lower air pressure cools the air enough to condense water vapor in the air into tiny water droplets.

How a waterspout formsThe first sign, which can be seen from the air but usually not from a boat, is the formation of a dark spot on the ocean. Smoke flares dropped in these areas show the air is moving in a circle and upward. Many dark spots die out without progressing any further. But some begin to take on a spiral pattern of dark and lighter water.

At the second stage someone on a boat at the surface would probably feel the wind shift and maybe increase. Also, if you looked upward, you might see a funnel coming from a cloud overhead or off to one side.

People on boats will see the third stage.

Even though it might be invisible, a vortex is reaching the ocean surface from the cloud. When the wind speeds reach around 40 mph, the wind begins to kick up spray in a circular pattern -- the spray vortex. At this time you might see the funnel pointing down from the cloud toward the ring.

The fourth, or mature, stage is when the funnel reaches all the way from the cloud to the ocean. You can usually see through the funnel - it's really a thin cloud of tiny water droplets.

During this stage, small waves are being kicked up and the spout leaves a bubbly wake behind as it moves across the ocean. These tiny bubbles could be carbon dioxide and other gases that are dissolved in the water that are caused to effervesce by the low air pressure in the spout's center - like a bottle of soda that's just opened.

In the fifth, and final stage, the spray vortex weakens and the funnel becomes shorter and maybe more tapered. It often twists around and the bottom of the waterspout may move out from under the cloud.